This invention relates generally to electric circuit boards and more specifically to circuit boards having high voltage, high current, such as 240 volts, 50 amps, traces thereon.
It is conventional to have high voltage, high current lines directly connected to relays and to use a relatively low voltage, low current signal to effect energization of the relay and concomitantly energize or de-energize the high voltage, high current lines. By way of example, in switching loads such as those used for residential heating, high voltage, high current lines are connected through relays to banks of electric heaters with the relays energized by appropriate low voltage signals from a thermostat or the like.
A control system for energizing and de-energizing electric heater banks along with associated components such as a fan, in which high voltage, high current lines are directly coupled to traces on a circuit board and to relays mounted on the board is shown in copending application Ser. No. 07/886,274 assigned to the assignee of the present invention. In that application a method and apparatus is disposed in which extended relay contact life is obtained by using a microprocessor, reading the AC input signals when the wave is at a peak, generating an output from the microprocessor to a relay at a time equal to a delay following a zero crossing of the AC line current wave so that contact engagement occurs in the proximity of zero crossing of the AC line current. This near zero crossing of the AC line current is conducive to providing the high voltage, high current traces directly on the board for connection with the relays.